This invention relates to a process for separating a polymerization catalyst from a polymer. More particularly, this invention relates to a method for removing alkali metal catalyst contaminants, particularly lithium methoxide, from an anionically polymerized hydroxy-terminated conjugated diene polymer.
Alkali metals, particularly lithium, have long been used in catalysts to promote anionic polymerization of conjugated dienes. Heretofore, several methods have been proposed for separating such compounds from a polymer, particularly a conjugated diolefin polymer. In general, these methods involve contacting the polymer and the alkali metal containing composition with water and/or an acid. A principal problem associated with these methods is that each introduces an impurity to the polymer which must be removed before the polymer is suitable for at least most end use applications. These methods, then, add a rather complicated separation step to the process. U.S. Pat. No. 5,177,297 describes how a magnesium phosphate compound can be used to remove lithium contaminants from conjugated diene polymers, specifically copolymers thereof with vinyl aromatic hydrocarbons. U.S. Pat. No. 4,855,409 describes how the same magnesium phosphate compounds can be used to remove alkali metals from polyols. However, these materials have been proven ineffective in removing lithium contaminants from hydroxy-terminated conjugated diene polymers and therefore, there is a need for a method for removing alkali metal, especially lithium, contaminants from such hydroxy-terminated polymers. The present invention provides such a method.